I. Field
The invention relates generally to the field of wireless communications, and more particularly to a method, apparatus, and system for selectively responding to incremental redundancy transmissions in multiple access communication systems.
II. Background
In recent years, communication systems' performance and capabilities have continued to improve rapidly in light of several technological advances and improvements with respect to telecommunication network architecture, signal processing, and protocols. In the area of wireless communications, various multiple access standards and protocols have been developed to increase system capacity and accommodate fast-growing user demand. These various multiple access schemes and standards include Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Code Division Multiple Access (CDMA), and Orthogonal Frequency Division Multiple Access (OFDMA), etc. Generally, in a system which employs TDMA technique, each user is allowed to transmit information in his assigned or allocated time slots whereas an FDMA system allows each user to transmit information on a particular frequency that is assigned to that particular user. A CDMA system, in contrast, is a spread spectrum system which allows different users to transmit information at the same frequency and at the same time by assigning a unique code to each user. In an OFDMA system, a high-rate data stream is split or divided into a number of lower rate data streams which are transmitted simultaneously in parallel over a number of subcarriers (also called subcarrier frequencies herein). Each user in an OFDMA system is provided with a subset of the available subcarriers for transmission of information. The subset of carriers provided to each user in an OFDMA system can be fixed or vary, for example, in the case of Frequency-Hopping OFMDA (FH-OFDMA). Multiple access techniques in TDMA, FDMA, and CDMA are illustrated in FIG. 1. As shown in FIG. 1, the communication channels in FDMA are separated by frequencies in which a particular channel corresponds to a particular frequency. In a TDMA system, the communication channels are separated by time in which a particular channel corresponds to a particular time slot. In contrast, communication channels in a CDMA system are separated by codes in which a particular channel corresponds to a particular code.
In wireless systems, it is usually inefficient to guarantee a reliable packet transfer on every single transmission. The inefficiency is particularly pronounced in systems where underlying channel conditions vary drastically from transmission to transmission. For example, in an FH-OFDMA system, there is a wide variation in the received signal-to-noise ratio (SNR) between frames/packets, thus making it difficult and inefficient to guarantee a small frame error rate (FER) for each packet transmission. Such difficulty and in-efficiency also apply to other communication systems which employ orthogonal multiple access techniques including, but are not limited to, TDMA, FDMA, and orthogonal CDMA, etc.
In such communication systems, a packet retransmission mechanism such as the Automatic Retransmission/Repeat Request (ARQ) scheme may be used to help lessen such inefficiency. However, this is done at the expense of higher packet latency since it takes longer on average for each packet to get through. In general, large packet latency may not be a significant problem for data traffic but could be detrimental to voice traffic or other types of applications that require low latency in transmission of information. Moreover, packet transmission latency is expected to increase as the number of users in the system continues to grow. Thus, to improve system capacity (e.g., based on system throughput or number of users that simultaneously use the system, etc.), transmission latency should be kept low or small.
The efficiency of early termination in ARQ schemes is based on the reliability of acknowledge (ACK) and not-acknowledge (NACK) transmissions. If the error rates of NACKs sent that are interpreted as ACKs becomes too great, then many packet transmissions will be incorrectly terminated prior to success. Further, access terminals may needlessly be sending ACK/NACK messages, thereby causing interference in the system.
Accordingly, there exists a need for a method, apparatus, and system for reducing overhead in responding to ACK/NACK messages in multiple access systems that employ packet retransmission mechanisms such as ARQ.